1. Field of the Invention
The present invention relates to a sliding type bushing which is suitably used as a suspension bushing of a motor vehicle, for example, and which is capable of effectively preventing transmission of vibrations while absorbing an input load applied in a torsional or circumferential direction about the axis of the bushing.
2. Discussion of the Prior Art
There is known a rubber bushing for connecting a suspension arm in a vehicle suspension system, to a support member fixed to a vehicle body or a wheel support member, in a vibration damping manner, such that the suspension arm is pivotable about the axis of the support member. The known rubber bushing includes an inner and an outer metallic sleeve which are disposed in coaxial and radially spaced-apart relation with each other, and a cylindrical elastic body interposed between the inner and outer sleeves for flexible connection therebetween. The rubber bushing is adapted to absorb input vibrations applied in a radial direction perpendicular to the axis of the bushing, based on an elastic property of the elastic body. Further, the known bushing permits the inner and outer sleeves to be rotated relative to each other about the axis of the bushing, based on torsional deformation of the elastic body about the axis.
However, the stiffness of the thus constructed bushing measured in the radial direction, and the torsional stiffness thereof measured in the circumferential direction are both determined by the elasticity and configuration of the elastic body. Therefore, it is rather difficult to determine degrees of the stiffness in the radial and circumferential directions independently of each other, depending upon the required spring characteristics of the bushing. Accordingly, it is extremely difficult for the known suspension bushing to exhibit the two different characteristics required for the recent motor vehicles, that is, provide sufficiently reduced stiffness in the circumferential direction so as to improve a driving comfort of the vehicle, while providing a sufficiently high degree of stiffness in the radial direction so as to assure excellent stability and controllability of the vehicle.
In view of the above, there has been proposed a rubber bushing as disclosed in laid-open Publication No. 60-3335 of unexamined Japanese Utility Model Application. This rubber bushing has a cylindrical race which is secured to an inner or outer circumferential surface of the elastic body, and a separately formed resin sleeve which is interposed between the race and the inner or outer sleeve such that the resin sleeve is held in slidable contact with the race and the adjacent sleeve. In this arrangement, the rubber bushing exhibits a relatively low degree of torsional stiffness with respect to the input load applied in the circumferential direction thereof.
In the thus constructed rubber bushing, however, the separately formed resin sleeve is inserted in between the race and the inner or outer sleeve, and is axially gripped at its axially opposite end faces by and between respective retainer rings which are press-fitted on or in the inner or outer sleeve adjacent to the resin sleeve. Thus, the rubber bushing requires increased numbers of components and manufacturing steps, which inevitably push up the cost of the bushing. In addition, the rubber bushing suffers from reduced sliding capability, and unfavorable rattling displacements or excessive plays or clearances of the components thereof, which result from accumulated dimensional errors or a variation in the machining or forming accuracy which may arise during production of the resin sleeve, and the race and the inner or outer sleeve which are held in sliding contact with the resin sleeve. Thus, the conventional bushing cannot provide a sufficiently high degree of sliding capability.
In the rubber bushing as described above, the inner and outer circumferential surface of the resin sleeve function as sliding surfaces for slidable contact with the race and the inner or outer sleeve. Therefore, the slidability of the bushing is deteriorated if the resin sleeve is formed of a fiber reinforced resin material which contains glass fibers or other reinforcing fibers. Thus, it is hard to employ such a fiber reinforced resin as a material for the resin sleeve, so as to assure a sufficient resistance of the sleeve to the input load.